Buying SAN gear is hard work.  You have to compare vendors based on performance, capacity, reliability, ease of implementation, quality of support, and of course, price.  When I’m working with a client buying new storage, here’s the questions I have them ask each prospective storage vendor.

Q: If we buy SSD, SAS, and SATA drives, how does the tiering work?  Some vendors can automatically move data between fast and slow drives, while other vendors only allow this manually – if at all.  If the storage does all the work for you, find out what kind of reporting it offers – some tiering solutions will automatically use SSDs where possible, but you’ll want to know when it’s time to buy more drives for each tier.

Q: Is SSD used for caching or for storage? How much do you recommend?  There’s no wrong answer here, but listen to their recommendations.  This is often the fastest way to improve performance.  It’s going to be expensive, but that’s not part of the technical decision.

Q: Do you support active/active multipathing for both sending and receiving on a single LUN?  If you have just one 1TB volume, and you’ve got a handful of connections to the storage, can you use multiple connections simultaneously to get more throughput during read/write intensive operations?  Most vendors just don’t support this, so ask them to be as specific as possible – it’ll help you design the right connectivity for your storage.  No multipathing capabilities means your big databases may need 8Gb FC or 10Gb iSCSI connectivity, and they may need to be broken up across multiple files on multiple LUNs.

Q: Does the system include snapshots? Are they writable?  Do they integrate with SQL Server?  SAN snapshots are one of my favorite tricks to speed up multi-terabyte database backups.  We can take a snapshot of entire SAN volumes in a matter of seconds – but only if the vendor includes this support.  Some vendors include it, and some vendors charge an arm and a leg.

Q: Exactly how much can we grow before we have to make a major upgrade?  Storage gear is a lot like servers: if you need to get an incremental performance upgrade you may be able to throw in a few more drives, but if you need to double or quadruple your performance, you might get stuck replacing the whole thing.  Ask exactly how much cache, how many ports, and how many drives you can add before you have to make big changes.

Q: What are your best practices for Microsoft SQL Server?  Ask for their technical documentation on configurations.  They may not have an up-to-date version for SQL Server 2012, for example, but they should at least have a copy for 2005 or 2008.  Examine that documentation for things like RAID levels, multipathing, drive separation, and so forth, and take those guidelines into account as you spec out hardware.  If they don’t have guidelines for Microsoft SQL Server, ask for Oracle, but if they don’t have either of those, be aware that you’re going to be on your own for performance troubleshooting.

Q: How frequently have firmware upgrades come out in the last 6 months, and what’s the upgrade process like?  Insist on specifics from their technical documentation, not general sales and marketing info.  If they’re putting out firmware upgrades every few weeks, and if they recommend these upgrades in order to get support, and if you’re required to take all attached servers down in order to perform the upgrade, that’s a problem.  If, on the other hand, they recommend performing the upgrades online, administration will be much easier.  Insist on the specifics, though, because I’ve seen SAN vendors say, “Well, you could do the upgrade online…but we don’t recommend that.”

Q: Can I talk privately to a similarly-sized customer?  Ask for a nearby reference that you can have a private conversation with – without the storage vendor’s staff around.  Try to get someone technical from the reference company, not a C-level executive, because you want someone who’s working with this thing every day.  Ask about the company’s experience with performance, capacity, reliability, ease of implementation, and quality of support.  Do it in person, not over the phone or over email, because you’ll be more likely to get the off-the-record truth.  Ask them, “If you were going to do it all over again, would you buy this product – or if you were going to buy something else, what would it be?”

After you’ve compiled everyone’s answers together, you should be able to narrow down the field to a few strong contenders.  From there, ask each vendor to provide access to a system similar to the one you’d be purchasing.  If you’re spending enough money, either you can access the system remotely, or they’ll loan you a demo set of gear to install in your datacenter.  Asking the right questions ahead of time ensures that you’ll spend the least amount of time kicking the tires of gear that just won’t perform.